MADISON, Wis. -

The Dane County Medical Examiner has released the name of the man who died in an apartment fire at 6425 Bridge Road Wednesday afternoon.

Christopher G. Williams, 51, died from thermal injuries and smoke inhalation, according to a release. The death remains under investigation.

Firefighters were called to the Riverwood Apartments around 3:45 p.m.

The maintenance supervisor said four units will need to be repaired; two will need to be completely remodeled.

About 20 people have been displaced by the fire.

Most of the residents made it out of their apartments because the building had working smoke detectors, officials said.

"The original 911 call came from an apartment across the hallway from people who heard the smoke detector, and that's what sounded the alarm and the person across the hall called 911,” said Madison Fire Chief Steven Davis.

Davis said the building didn't have sprinklers because it was built before they were required.

Investigators are still trying to determine the total amount of damage to the apartment building and what started the fire in the first place.